OBJECTIVES: (1) Mitotic chromosomes. We shall continue the investigation on the arrangement of the chromatin fiber in mitotic chromosomes using whole mounts and thick sections with the million volt electron microscope. Early condensation stages will be studied using PCC (precociously condensed chromosomes) obtained by fusing G1 cells with mitotic cells. (2) The kinetochore of mammals will be further studied using mouse cell lines in culture. We have shown that the outer kinetochore disk represents a special arrangement of chromatin fibers looping out from the inner disk. These fibers behave differently to treatment with various salt solutions and we want to see whether they have the typical nucleosome structure as usual chromatin. The cup-and-ball kinetochore will be investigated with the same methods to study microtubule chromatin interaction in this type. Insects (roaches, grasshoppers) will be used. (3) Polytene chromosomes. Using mechanically isolated polytene chromosomes from footpads of sarcophaga, we shall extract H1 and total histones relate to DNA-histone-non-histone proteins to chromomere and band structure. Puffs induced by heat and anoxia will be used to study structural changes during initiation and regression of functional activity.